Someone

$maanantai = array_slice($events, 0, 6);
$tiistai = array_slice($events, 6, -18);
$keskiviikko = array_slice($events, 12, -12);
$torstai = array_slice($events, 18, -6);
$perjantai = array_slice($events, 24);

$_POST["maanantai"];
$_POST["tiistai"];
$_POST["keskiviikko"];
$_POST["torstai"];
$_POST["perjantai"];

$day = $_GET[""];